In fact, most American slaves were not kidnapped on another continent. Though over 12.7 million Africans were forced onto ships to the Western hemisphere, estimates only have 400,000-500,000 landing in present-day America. How then to account for the four million black slaves who were tilling fields in 1860? “The South,” the Sublettes write, “did not only produce tobacco, rice, sugar, and cotton as commodities for sale; it produced people.” Slavers called slave-breeding “natural increase,” but there was nothing natural about producing slaves; it took scientific management. Thomas Jefferson bragged to George Washington that the birth of black children was increasing Virginia’s capital stock by four percent annually.

Here is how the American slave-breeding industry worked, according to the Sublettes: Some states (most importantly Virginia) produced slaves as their main domestic crop. The price of slaves was anchored by industry in other states that consumed slaves in the production of rice and sugar, and constant territorial expansion. As long as the slave power continued to grow, breeders could literally bank on future demand and increasing prices. That made slaves not just a commodity, but the closest thing to money that white breeders had. It’s hard to quantify just how valuable people were as commodities, but the Sublettes try to convey it: By a conservative estimate, in 1860 the total value of American slaves was $4 billion, far more than the gold and silver then circulating nationally ($228.3 million, “most of it in the North,” the authors add), total currency ($435.4 million), and even the value of the South’s total farmland ($1.92 billion). Slaves were, to slavers, worth more than everything else they could imagine combined.

Virginia slaveowners won a major victory when Thomas Jefferson’s 1808 prohibition of the African slave trade protected the domestic slave markets for slave-breeding.

I haven’t read the book, but I imagine they touched on the fact that by growing slave populations, southern states were literally manufacturing more political representation due to the Three-Fifths clause in the US Constitution. They bred more slaves to help politically safeguard the practice of slavery.

In the 1830s, powerful Southern slaveowners wanted to import capital into their states so they could buy more slaves. They came up with a new, two-part idea: mortgaging slaves; and then turning the mortgages into bonds that could be marketed all over the world.

First, American planters organized new banks, usually in new states like Mississippi and Louisiana. Drawing up lists of slaves for collateral, the planters then mortgaged them to the banks they had created, enabling themselves to buy additional slaves to expand cotton production. To provide capital for those loans, the banks sold bonds to investors from around the globe — London, New York, Amsterdam, Paris. The bond buyers, many of whom lived in countries where slavery was illegal, didn’t own individual slaves — just bonds backed by their value. Planters’ mortgage payments paid the interest and the principle on these bond payments. Enslaved human beings had been, in modern financial lingo, “securitized.”

As historian Edward Baptist reveals in The Half Has Never Been Told, slavery and its expansion were central to the evolution and modernization of our nation in the 18th and 19th centuries, catapulting the US into a modern, industrial and capitalist economy. In the span of a single lifetime, the South grew from a narrow coastal strip of worn-out tobacco plantations to a sub-continental cotton empire. By 1861 it had five times as many slaves as it had during the Revolution, and was producing two billion pounds of cotton a year. It was through slavery and slavery alone that the United States achieved a virtual monopoly on the production of cotton, the key raw material of the Industrial Revolution, and was transformed into a global power rivaled only by England.